Electrochemical machining (ECM) is a well known process for machining metallic based workparts and in the past has been employed to machine complex airfoil shapes on individual blades and complex airfoil blades attached to a central cylindrical hub and extending radially therefrom around its periphery.
ECM apparatus for machining individual airfoils projecting from the central hub of an integral bladed gas turbine engine rotor or wheel is shown in the Stark et al U.S. Pat. No. 3,523,876 issued Aug. 11, 1970; the Stark al U.S Pat. No. 3,714,017 issued Jan. 30, 1973; and the Kawafune et al U.S. Pat. No. 3,803,009 issued Apr. 9, 1974. In these patents, the airfoils are completely machined by the ECM process out of a cylindrical blank or disc of material.
Tne Trager U.S. Pat. No. 3,288,699 issued Nov. 29, 1966 illustrates an ECM apparatus for machining in simultaneous fashion multiple airfoils integral on a turbine wheel blank or disc wherein during axial advance of the cathode the workpart (turbine wheel blank) is rotated through a selected angle to impart a curve to the airfoils as they are formed by the cathode.
The Lucas U.S. Pat. No. 3,970,538 issued July 20, 1976 describes an ECM apparatus for mcchining oversize leading and trailing edges of airfoil blades integrally cast with a central hub to form an integral bladed rotor for a gas turbine engine. A special cathode structure is disclosed to ECM the leading and trailing edges.
Other prior art workers have employed ECM apparatus to machine a plurality of airfoil blades from one piece of elongated stock material or individual airfoils one at a time For Example, the Wilson et al U.S. Pat. No. 4,256,555 issued Mar. 17, 1981 illustrates ECM'ing an individual airfoil shaped blade preform using opposed cathodes which are caused to move toward opposite sides of the blade preform by movable arms or rams on a conventional machine. In the past, a ball screw assembly driven by a servomotor has been employed to drive each ram with the cathode thereon. In the patent, the cathode rams are driven in opposed directions at a 45.degree. angle relative to the centerline of the blade. The Goodwin U.S. Pat. No. 3,309,294 issued Mar. 14, 1967 illustrates an ECM apparatus for shaping an individual metallic airfoil blade for an axial flow compressor of a gas turbine engine.
The Schrader U.S. Pat. No. 4,052,284 issued Oct. 4, 1977 illustrates an ECM apparatus for at least partially forming a plurality of airfoils in a workpart. The apparatus includes a plurality of separately movable electrodes, each pair of electrodes being movable along paths defining an acute angle relative to the sides of the workpart. The Schrader U.S. Pat. No. 4,057,475 issued Nov. 8, 1977 describes a ECM method for forming a plurality of airfoils in a single workpiece. The Schrader et al U.S. Pat. No. 4,167,462 issued Sept. 11, 1979 describes a control system for an ECM machine having a plurality of electrodes driven by a plurality of identical hydraulic pumps.
The Broat et al U.S. Pat. No. 3,515,659 issued June 2, 1970, discloses an electrochemical machine for machining an individual airfoil wherein fluid actuated members each carrying a sealing member are slid against opposite sides of a cathode toward and into sealing engagement with the opposite ends of the airfoil and, in combination with other components, seal off the cavity in which the airfoil is disposed to enhance electrolyte velocity. However, the fluid actuated sealing members slide in the same direction as that of relative movement between the cathode and airfoil being machined. The fluid actuated members are not balanced as far as electrolyte pressure is concerned.
The Sanders U.S. Pat. No. 3,060,114 issued Oct. 23, 1982 discloses an ECM machine and method using a reciprocating cathode structure. The Inoue U.S. Pat. No. 4,504,721 issued Mar. 12, 1985, illustrates a multiple axes electrical discharge machine for forming a three dimensional cavity in a workpart.
Copending patent application Ser. No. 021,699 filed Mar. 4, 1987, entitled "Electrolyte Chamber With Cathode Sealing Means For ECM Machining" in the name of Edmund R. Hinman as inventor discloses an electrolyte chamber having a pair of cathodes movable in the chamber toward a workpart so as to machine same and a respective sealing piston movable toward a respective cathode in a direction transverse to cathode movement toward the workpart so as to be placed in sealing relation to the respective cathode. The sealing pistons substantially close off a respective clearance space between each cathode and wall of the electrolyte chamber. However, there is no means disclosed for balancing electrolyte pressure on the sealing pistons.